StarDate Podcast

Edwin Hubble gets the credit for discovering that the universe is expanding. But that finding was made possible by work done by Vesto Slipher. He was the first to measure the motions of distant galaxies – the key to Hubble’s discovery. Slipher was born 150 years ago today, in Mulberry, Indiana. He worked on the family farm, and developed an interest in astronomy. A college professor helped him get a job as an assistant at Lowell Observatory in Arizona, where he worked for the next five decades. Slipher studied what were called “spiral nebulae.” It wasn’t certain whether these pinwheels were motes of matter in the Milky Way, or “island universes” of stars outside the Milky Way. Slipher used a technique that splits an object’s light into its individual wavelengths. The object’s motion shifts those wavelengths. Objects that are moving away from us are shifted to longer, redder wavelengths. Slipher found that most of the spirals were moving away from us in a hurry. He suggested the objects were far outside the Milky Way. But he couldn’t prove it because he had no way to measure the distances. Hubble did measure the distances, proving that the spirals are separate galaxies. He then combined Slipher’s observations with his own to show that the farther a galaxy, the faster it was moving. Later, astronomers concluded that the universe is expanding – a finding made possible in large part by Vesto Slipher. Script by Damond Benningfield

There’s nothing in the night sky quite like the Pleiades. The star cluster forms a tiny dipper. Depending on sky conditions and the viewer’s eyesight, anywhere from a half dozen to a dozen stars or more are visible to the naked eye. Its unique visage has made the Pleiades one of the most important sky objects in many cultures. The people of the Andes timed the start of the harvest season to its first appearance in the dawn sky. The Aztec year began at about the same time. In Hawaii, the Pleiades was known as Makali’i. And the year began when Makali’i first appeared in the evening twilight – the middle of November. The year, the new year, and a festival period shared a name: Makahiki. The customs varied from island to island. But they had a lot in common. The celebration lasted for several months. Warfare and most work were banned. Instead, people danced, feasted, played sports, and reconnected with family and friends. And they made offerings to Lono, a god of agriculture, music, and peace. The Pleiades is just climbing into the evening twilight, in the east-northeast, across Hawaii and most of the rest of the country. In some Hawaiian traditions, Makahiki doesn’t begin until the first appearance of the crescent Moon in the west after the Pleiades returns. That’s coming up on the 21st – the start of the new year and the celebration that honors it. Hau’oli makahiki hou! – Happy New Year! Script by Damond Benningfield

The Moon shoots the gap between some bright companions tonight: the planet Jupiter and the star Pollux, the brighter “twin” of Gemini. They climb into good view by about 10:30 or 11, and stand high overhead at dawn tomorrow. Jupiter is the largest planet in the solar system, and it has the most turbulent atmosphere. Hurricane-like storms as big as continents twirl across it. Thunderstorms can produce lightning bolts far more powerful than any on Earth, as recorded by a passing spacecraft. And the storms might produce their own giant hailstones: “mushballs” as big as softballs. The idea was first proposed in 2020. And a study published earlier this year supports it. The study used observations by the Juno spacecraft, which is orbiting Jupiter, along with Hubble Space Telescope and a radio telescope on Earth The study says the mushballs may begin as droplets of frozen water far below the cloud deck. They get caught in updrafts that howl at 200 miles an hour. They’re carried to the tops of the clouds, which can be tens of miles thick. Along the way, the ice mixes with ammonia, forming a slushy liquid. When the balls get heavy enough, they begin to drop. As they descend, they’re coated with fresh ice, giving them a hard shell around a slushy middle – mushballs. The mushballs plunge hundreds of miles below the clouds, where they vaporize – “mushing” into the depths of the giant planet. Script by Damond Benningfield

In the early 20th century, scientists discovered a mysterious new type of radiation. The higher they went, the stronger it became. They realized that it came from beyond Earth. And 100 years ago tomorrow, it got a name: cosmic rays. Nobel Prize winner Robert Millikan had become fascinated by the rays from outer space in the early ’20s. He coined the name “cosmic rays” in a paper about them, which he presented to a meeting on November 9th, 1925. Millikan thought the rays were a form of energy produced by matter that was being born in the space between the stars. Others disagreed, especially Arthur Compton – a future Nobel Prize winner himself. He argued they were subatomic particles racing through the universe at almost the speed of light. Compton was right. Cosmic rays are electrons, protons, or the nuclei of atoms. Most of the ones that hit Earth are produced by the Sun. But others come from far beyond our own solar system – and even from beyond our galaxy. The most energetic ones come from exploding stars, or from the violent regions around black holes. Most of these distant cosmic rays are blocked by the Sun or by Earth’s magnetic field. But a few enter the atmosphere. They strike atoms and molecules in the air, creating “showers” of other particles. If a shower occurs above the right kind of clouds, it can create lightning – a terrestrial light show with an extra-terrestrial origin. Script by Damond Benningfield

Nothing can survive the brutal conditions on the surface of the Moon. But a story that debuted 125 years ago depicted a vast civilization below the surface – a society of insects. First Men in the Moon was written by H.G. Wells. It was published over several months in two magazines – “The Cosmopolitan” in the United States, and “The Strand” in Britain. The first installment appeared in November of 1900. In the story, a man named Bedford befriends a scientist named Cavor who’s invented “cavorite” – a substance that nullifies gravity. He builds a ship and covers it with shutters that are coated in the stuff. Opening and closing the shutters allows the ship to move through space. The two men travel to the Moon, where they’re taken underground by the Selenites. Bedford escapes. Thinking Cavor is dead, he returns to Earth alone. But two years later, Cavor starts beaming messages to Earth. He describes the Moon and its inhabitants in detail. After he tells the Selenite’s leader of Earth’s war-like tendencies, though, he’s cut off – and never heard from again. First Men in the Moon was a hit. It influenced scientists and other fiction writers alike for decades, inspiring more stories, plus efforts to reach the Moon – a world populated only in the imagination. The Moon climbs into good view by about 8 o’clock tonight. Elnath – the second-brightest star of Taurus – is quite close to the Moon’s upper left. Script by Damond Benningfield

The black hole at the heart of the Milky Way is like the monster lurking under your bed. It’s four million times the mass of the Sun, and about 15 million miles across – just waiting to gobble up anything that gets too close. But compared to the black holes in many other galaxies, the one in the Milky Way is less like a monster and more like a dust bunny. The largest ones yet seen are thousands of times bigger. They’re known as ultra-massive black holes. Informally, they’re also called SLABs – stupendously large black holes. Just which one is the biggest is uncertain – it’s hard to measure the mass of something that might be billions of light-years away. A recent candidate is in a structure known as the Cosmic Horseshoe. The gravity of a stupendously large galaxy “warps” the view of a galaxy behind it, creating what looks like a big, blue horseshoe. In a recent study, astronomers combined a couple of techniques to measure the mass of the black hole in the foreground galaxy: 36 billion times the mass of the Sun. Researchers say the combo makes the measurement the most accurate for any candidate for the “biggest black hole” honors. But other black holes could be bigger. The biggest candidate is known as Phoenix A. It could be up to about 25 thousand times the mass of the Milky Way’s black hole. But that number is highly uncertain. So the search for the biggest black hole continues. Script by Damond Benningfield

A Little Red Dot might have a big black hole in its heart. And that’s a bit of a challenge to explain. Little Red Dots are galaxies from the first 1.5 billion years of the universe. The name comes from their appearance – they’re small and red, but they’re especially bright. They don’t appear to have enough stars to make them so bright. So a good bit of their “shininess” could come from giant black holes that are devouring material around them. As they tumble inward, the hot gas, dust, and stars produce enormous amounts of energy. Even so, the black hole in one Little Red Dot is a bit of a puzzler. Led by astronomers at the University of Texas at Austin, a team looked at CAPERS-LRD-z9 with Webb Space Telescope. By measuring the speed of material orbiting the center of the galaxy, the team determined that the black hole is up to 300 million times the mass of the Sun. And that’s where the challenge comes in. The galaxy is so far away that we see it as it looked when the universe was just 500 million years old – three percent of its current age. That makes the black hole the most-distant yet seen. But theories of how such monster black holes form say that half a billion years probably isn’t long enough to make one that big. So theorists have a lot of work to do to explain the giant black hole at the center of a Little Red Dot. More about black holes tomorrow. Script by Damond Benningfield

With the autumn harvest safely stowed away, many people in bygone centuries turned their attention to hunting. And just as the Harvest Moon helped them bring in the crops, the Hunter’s Moon helped them find game. The moonlight made it easier to track animals through the empty fields and beyond. Although most present-day Americans don’t have to worry about storing food for the winter, we still keep the names for those full Moons. We had the Harvest Moon last month. And tonight, it’s time for the Hunter’s Moon. The names for both of these full Moons come mainly from parts of Europe and the British Isles. The names were recorded as far back as the early 1700s, but they’d probably been in everyday use for much longer. Variations of the “Hunter’s Moon” label were used by several native tribes and nations in the Americas as well. The Harvest Moon is usually defined as the full Moon closest to the autumn equinox. Most years, that puts it in September. But this year, October’s full Moon edged out September by just a few hours. So the Hunter’s Moon got bumped into November. Officially, the Moon will be full at 7:19 a.m. Central Standard Time tomorrow. So it will appear almost as “full” when it rises tomorrow night as it does tonight – extra time to appreciate the brilliant glow of the Hunter’s Moon. Tomorrow: A giant black hole at the center of a little red dot. Script by Damond Benningfield

In 1908, a space rock the size of a small office building exploded above Siberia, flattening hundreds of square miles of forest. In 1975, several “fireballs” blazed across the night, and instruments on the Moon recorded several impacts. And 30 years later, scientists saw an impact on the Moon. These events might all be related to the Taurid meteor shower, which is underway now. The shower is created by two objects – a comet and an asteroid. They might be the remnants of a larger body that broke apart thousands of years ago. The debris might include larger rocks ranging from the size of boulders to mountains. The material is spaced across a long, wide path. Earth flies through this path twice a year. We sweep up some of the debris – mostly small bits of dust and rock. The amount of material varies from year to year, depending on which part of the stream we pass through. Right now, we’re in a thin region. In 1975, we passed through a denser part, producing more fireballs. It’s been suggested that when we pass through denser parts of the stream, we might encounter some of the bigger rocks, which could cause major damage if they hit us. Astronomers will be watching during the next crossings through dense regions, in the next decade. For now, the Taurids are at their best the next few nights. The Moon will wash out almost all the meteors. But a few fireballs might shine through. Script by Damond Benningfield

The Taurid meteor shower has a double identity. It’s split into two different streams, which peak a few nights apart in early November. Neither stream is particularly impressive, but things pick up when they overlap. Their story begins thousands of years ago, with the breakup of a big ball of ice and dust – Comet Encke. The biggest remaining chunk kept that name. But the breakup created several other big pieces, plus clouds of dust. The whole messy bunch is known as the Encke Complex. The southern Taurid stream consists of small bits of dust and rock shed by Encke itself. The northern stream is produced by one of its offspring – an asteroid that wasn’t discovered until 2004. Both streams contain a lot of debris, but it’s spread across tens of millions of miles. So it takes Earth weeks to fly through the streams. That means the twin showers last a long time, but they’re not usually all that noteworthy – at best, they produce no more than a handful of meteors per hour. Things are a little busier when the showers overlap, as they’re doing now. Unfortunately, the Moon will be full in a couple of days, so it’ll overpower almost all of the Taurids. The streams do produce a few especially bright meteors, but that’s about the best we can expect from the shower with a dual identity. The Taurid Complex may include some especially big, dangerous chunks of debris, and we’ll talk about that tomorrow. Script by Damond Benningfield

AUDIO: We have contact. We have initial contact – initial contact of the Soyuz capsule with the Expedition 1 crew to the International Space Station. A key milestone in the human exploration of space took place 25 years ago tomorrow. The first permanent crew took up residence in the International Space Station. And people have been living on the station ever since. They weren’t the first to actually visit the station. Several groups of astronauts and cosmonauts had spent time assembling the early pieces of the station. And by November 2000, it was ready for full-time occupancy. The Expedition 1 crew was commanded by American astronaut Bill Shepherd, and included Russian cosmonauts Sergei Krikalev and Yuri Gidzenko. They launched on October 31st, from Kazakhstan: AUDIO: 4, 3, 2, 1, we have ignition – we have ignition and liftoff. Liftoff of the Soyuz rocket, beginning the first expedition to the International Space Station and setting the stage for permanent human presence in space. After arrival, they had a lot of work to do to get the station ready, as Shepherd described a decade later: SHEPHERD: So the first week was really living in a sleeping bag, running around with a checklist and a bunch of tools, trying to get this stuff all to get cranking. Shepherd and crew spent more than four months getting the station cranking. Since then, almost 300 people from more than two dozen countries have lived and worked there – an unbroken presence in space. Script by Damond Benningfield

Like other buildings, observatory domes can outlive their usefulness. They may not be big enough for the latest telescopes. The light from encroaching cities can make it hard for them to see the heavens. Or time may just catch up to them. Many domes and related buildings have been torn down. Others have been converted into offices or libraries. And still others have been abandoned – left to the elements and the ravages of time. Several of these buildings are scattered around the country – in places like Illinois and the woods of Michigan, for example. Their walls are covered with graffiti, their floors with water and trash, their spaces haunted by the ghostly memories of nights under the stars. Perhaps the most famous abandoned observatory sits on a grassy knoll in Cleveland. It was built by the men who founded Warner and Swasey, a machine-making company. They were amateur astronomers who devoted part of their business to building telescopes – including the first big telescope at McDonald Observatory. In 1919, they donated an observatory to Case University. They equipped it with a telescope of their own making. Bigger telescopes followed. The beautiful building was abandoned in 1982. Its telescopes had been sent elsewhere, and its staff moved into other quarters. Today, the building is decaying and dangerous – a ghostly presence beneath the stars on Halloween night. Script by Damond Benningfield

The night sky is filled with monsters. And none are more fearsome than the Gorgons – three sisters who were so hideous that a single glance at them turned the observer to stone. One of them was beheaded by Perseus the hero. His constellation shows him holding the head, which is outlined by four stars – the Gorgons. In mythology, two of the sisters were immortal. But the third, Medusa, was not. Perseus managed to lop off her head with the help of the gods. They gave him an invisibility cloak, a diamond sword, and a bronze shield. He could safely view the Gorgons by looking at their reflection in the shield. Perseus used Medusa’s head to destroy the sea monster, Cetus, which was about to kill the princess Andromeda. Cetus and Andromeda have their own constellations, as do Andromeda’s parents. The brightest star in Medusa’s head is Algol – a name that means “head of the demon.” It’s low in the northeast in early evening and climbs high across the sky later on. The other Gorgons form an arc to the right of Algol. One is fairly easy to spot, while the other two require a darker sky. All four of the Gorgon stars are bigger, heavier, and brighter than the Sun. Algol is a couple of hundred light-years away, while the other three are about a hundred light-years farther. The Gorgons form a demonic presence in the sky – shining down on Halloween weekend. We’ll have more about Halloween tomorrow. Script by Damond Benningfield

A young “cotton-candy” planet is hastening its own demise. As it dips close to its star, it appears to trigger giant explosions that erode the planet’s atmosphere. The planet orbits HIP 67522, a star roughly 400 light-years from Earth. The star is a little bigger and heavier than the Sun, but less than one percent the Sun’s age. Such young stars generate strong magnetic fields. Lines of magnetic force tangle and snap, producing powerful flares. The planet, HIP 67522 b, orbits just a few million miles from the star, so it already receives hefty doses of radiation and charged particles. A European space telescope, Cheops, has seen 15 flares that are tied to the planet’s orbit around the star. The planet may gather magnetic energy as it whips around the star. Waves of magnetic force ripple outward like the wake of a ship. When the waves hit a stormy spot on the star, they trigger a giant flare. That douses the planet with six times more radiation than it would receive otherwise. HIP 67522 b is almost as big as Jupiter, the giant of our own solar system. But it’s only about one-quarter of Jupiter’s mass. That makes the planet especially puffy, like cotton candy. But as it’s zapped by the star, some of its atmosphere is blown away. In a hundred million years or so, it could shrink to less than half its current size – a shrinkage caused by its close orbit around the star. Script by Damond Benningfield

A visitor from far beyond the solar system is getting better acquainted with the Sun this week. Tomorrow, it’ll make its closest approach to the Sun – just 126 million miles. After that, it’ll head back toward interstellar space. The visitor is 3I/ATLAS. It was discovered on July 1st by an automated telescope that looks for comets and asteroids. Calculations of its orbit quickly showed that it came from outside the solar system. That makes it the third known visitor from interstellar space. It originated in the galaxy’s “thick disk.” That’s a region that sandwiches our part of the disk. It contains stars that are far older than the Sun. Estimates say 3I/ATLAS could be three billion years older than the solar system, so it could preserve a chemical record of an earlier era in galactic history. 3I/ATLAS is a comet – a ball of rock and frozen gases a few miles in diameter. As it’s closed in on the Sun, some of its gas has vaporized, releasing bits of dust as well. Observations will reveal the composition of this material, telling astronomers about conditions in the region where it formed. Unfortunately, astronomers can’t see 3I/ATLAS at all right now – it’s hidden in the Sun’s glare. It’ll return to view in December – but only when viewed through a telescope. It’ll pass closest to Earth on December 19th – almost 170 million miles away. Script by Damond Benningfield

Big “wobbles” in Earth’s magnetic field more than 40,000 years ago could have made the cultures of the time feel wobbly as well. Early modern humans might have adapted to the wobbly field better than Neanderthals. Earth’s magnetic field protects the surface from high levels of solar radiation. But during a period known as the Laschamp Excursion, which began 42,000 years ago, the field weakened to just 10 percent of its current intensity. And instead of acting like a bar magnet, with strong north and south poles, it generated smaller poles all across the planet. As the field wobbled, it produced brilliant auroras in regions where they had seldom been seen. It also allowed more radiation to zap the upper atmosphere. That destroyed some of Earth’s protective ozone. It also changed climate patterns across the planet. This turbulent period lasted about 1800 years. A new study found changes in the behavior of Neanderthals and modern humans in Europe and Asia during this period. The changes suggest these cultures were trying to protect themselves from the dangers of the weakened field, including sunburn, higher rates of skin cancer, and eye damage. The early humans apparently adjusted better than Neanderthals. Many factors were involved in the behavioral changes. Even so, researchers say the Lashcamp Excursion might have spurred early humans to respond to their changing environment. Script by Damond Benningfield

As seen from most of the United States, the Big Dipper is plunging toward the northern horizon as night falls, as if it’s about to dip into a pail of water. If you line up the stars at the outer edge of the dipper’s bowl, and follow that line to the upper right, the first moderately bright star you come to is Polaris, the Pole Star or North Star. Earth’s north pole aims toward it, so Polaris forms the hub of the northern sky – all the other stars appear to rotate around it. And it’s always at the same point above the horizon – night and day, all year long. There’s a southern pole star, too. It’s not as prominent as Polaris, though. In fact, it’s barely visible. The star is Polaris Australis. It’s also known as Sigma Octantis because it’s in the constellation Octans, which depicts a navigational instrument known as an octant. Polaris Australis isn’t as impressive as Polaris mainly because Polaris is huge and brilliant. Compared to most stars, though, the southern pole star is impressive, too. It’s more than half again the mass of the Sun. It’s expanding as it nears the end of its life, so it’s several times wider than the Sun. And its outer layers puff in and out, so it brightens and fades a tiny bit every couple of hours. On average, it’s more than 40 times brighter than the Sun. But it’s almost 300 light-years away. So that keeps Polaris Australis from being a better pointer to the celestial south pole. Script by Damond Benningfield

The Blue Danube has been performed for some pretty lofty audiences – kings and queens, emperors and empresses, presidents and prime ministers. But a performance earlier this year topped them all: it was aimed at the stars. The waltz was composed by Johann Strauss II, who was born 200 years ago today. His birthday was one of the motivations for the performance. The other was the 50th anniversary of ESA – the European Space Agency. So the broadcast was mostly symbolic – not a real attempt to contact other civilizations. The waltz was performed by the Vienna Symphony Orchestra in late May. It was transmitted to space by one of ESA’s tracking stations. The waltz was beamed toward Voyager 1. It’s the most-distant working spacecraft in history – more than 15 billion miles from Earth – so far that it took 23 hours for the waltz to reach it. Voyager carries a golden phonograph record inscribed with several musical works – but not the Strauss waltz. Voyager is passing through Ophiuchus, near the constellation’s brightest star, Rasalhague. It’s about half way up in the west-southwest at nightfall, and it’s easy to see. It’s a bit more than 48 light-years away. So if anyone there happens to point a radio telescope toward Earth in late 2073, perhaps they’ll hear the strains of The Blue Danube waltzing through the galaxy. Script by Damond Benningfield

A giant companion to a giant star faces an uncertain fate. The star is dying. As it expires, it will blast the companion, drag it inward, zap it with radiation, then loosen its grip on whatever remains. Mirach is the second-brightest star of Andromeda. It’s passed through the prime phase of life, and now is in the red-giant phase. It’s puffed up to about 85 times the diameter of the Sun, making it shine about 1700 times brighter than the Sun. Two years ago, astronomers discovered that Mirach has a companion. It’s probably a “failed star” known as a brown dwarf. It’s twice as far from Mirach as Earth is from the Sun. Before long – astronomically speaking – the star’s outer layers will flow into space at tens of thousands of miles per hour. That will “sandblast” the companion, stripping away some of its bulk. And friction from that material will drag the companion toward the star. After that, only the star’s hot but dead core will remain – a white dwarf. It’ll pelt the companion with ultraviolet radiation, vaporizing more of it. But the white dwarf will be much less massive than the present star, so it will loosen its gravitational grip on the companion. No one knows for sure how all of this will play out, so we can’t predict the fate of Mirach’s giant companion. Mirach is a third of the way up in the east-northeast at nightfall. It’s easy to see, even from most light-polluted cities. Script by Damond Benningfield

The black hole at the heart of a distant quasar has the biggest appetite astronomers have ever seen. It gobbles down the equivalent of one Sun per day – more than any other known black hole. It’s fed by the widest disk of gas and dust yet seen. And it outshines everything else in the known universe – 500 trillion times the Sun’s brightness. The quasar is so far away that we see it as it looked when the universe was a little more than one-tenth of its current age. It was discovered in the early 1980s, but astronomers thought it was a star. They deciphered its true nature just a couple of years ago. The heart of the quasar is a black hole 17 billion times the mass of the Sun. That’s not a record, but it’s near the top of the list. The black hole’s enormous gravity pulls in gas, dust, and stars. They form a spinning disk around the black hole. The disk is seven light-years across – half again the distance from the Sun to its closest neighboring star. As material in the disk funnels toward the black hole, it’s heated to millions of degrees. So the disk shines brilliantly – allowing us to see it across most of the visible universe. The quasar is in Pictor, the painter’s easel. For skywatchers in the far-southern United States, the constellation is barely in view, low in the south, before dawn. Despite the quasar’s great power, though, it’s much too faint to see without a telescope. Script by Damond Benningfield

We got our first picture from the surface of another planet 50 years ago today, when the Soviet Union’s Venera 9 landed on Venus. It transmitted data from the surface for 53 minutes, including a wide panorama. Venus is completely covered by thick clouds, so we can’t see its surface from Earth, or even from orbit around Venus – orbiters use radar to peer through the clouds. Venus also has a hot, dense atmosphere, so landing there is tough. Venera 9 parachuted through the clouds, measuring their thickness and composition. At the surface, it measured the density of the atmosphere – about 90 times the density of Earth’s atmosphere. And it measured the surface temperature – about 900 degrees Fahrenheit. The lander was supposed to take a full 360-degree view of the landscape. But the lens cap on one of its cameras didn’t pop off as planned, so Venera photographed only half of the scene around it. The image revealed a flat landscape covered with wide, flat rocks. And the lighting was comparable to a cloudy summer day on Earth. Venera 9 relayed its findings to Earth through an orbiter. Communication ended when the orbiter moved out of range – ending our first direct view of the surface of Venus. Venus is the beautiful “morning star” this month. It’s low in the east at dawn, and slowly fades from view in the waxing twilight. Tomorrow: the most ravenous black hole. Script by Damond Benningfield

A star in the constellation Cetus brightens and fades dramatically every 11 months. At its brightest, it’s fairly easy to see. At its faintest, it’s visible only through a telescope. Because of that change, a 17th-century astronomer called the star Mira – from the Latin word for “wonderful.” The star changes because it pulses in and out like a beating heart. Mira’s in the final stages of its red-giant phase of life. Its core is no longer producing nuclear reactions. Instead, it’s fusing hydrogen and helium in thin shells around the core. Mira’s outer layers are puffed up by radiation from the shells. At the maximum, that inflates the star to about 400 times the diameter of the Sun. That’s also when its surface is coolest and faintest. As the outer layers cool, they fall inward, making the surface hotter and brighter. At minimum, the star is about 330 times the Sun’s diameter. Each time it puffs up, Mira loses a little of the gas at its surface. Within the next million years or so, it’s likely to expel all the gas in its outer layers. That will leave only its hot but dead core – a white dwarf. Astronomers have discovered thousands of stars like Mira. And many others will undergo the same phase, including the Sun – in about six billion years. Mira climbs into view in the east by 8:30 or 9. But it’s in the “fading” part of its cycle, so you need a telescope to see it. Script by Damond Benningfield

Algol does something amazing. Every 2.9 days, the star fades to just one-third of its usual brightness. In centuries past, the stars were thought to be unchanging. A star that changed so blatantly was a bit scary. So it was given a name to match: “Algol” comes from an Arabic phrase that means “head of the demon.” But the star’s odd behavior isn’t scary it all – Algol fades as the result of eclipses. The system consists of three stars. Two of them form a tight binary. The members of the binary orbit each other once every 2.9 days. We see the system edge-on, so the two stars eclipse each other. One star is much brighter than the other. When the fainter star crosses in front of it, the system fades dramatically. When the bright star covers up the faint one, though, the difference is tiny – much too subtle to see with the eye alone. Astronomers have cataloged hundreds of eclipsing binaries. And the eclipses are important. They reveal the relative sizes and masses of the two stars, details about their orbit, and more. So there’s nothing to fear from these up-and-down star systems. Algol is low in the northeast at nightfall, in Perseus. It should be at its brightest tonight. The faint part of its cycle will happen during daylight for the next few cycles. It’ll be visible during nighttime later in the month. Sometimes, a star can change brightness all on its own, and we’ll have more about that tomorrow. Script by Damond Benningfield

The Orionid meteor shower should be at its most active the next few nights. And there’s no Moon to get in the way, so it should be a pretty good show. The shower is named for Orion because its meteors appear to “rain” into the sky from Orion the hunter. The constellation climbs into good view after midnight, so that’s when the shower is at its best – between midnight and dawn. You don’t have to look at Orion to see the meteors, though – they can blaze across any part of the sky. The meteors are bits of debris from Comet Halley. The comet sheds grains of dust as it orbits the Sun. When Earth crosses the comet’s path, some of those grains plunge into the atmosphere. They instantly vaporize, creating the streaks of light known as meteors. Most of the dust grains are no bigger than pebbles. But a few are larger. They form brilliant streaks that are visible even in a somewhat light-polluted sky. And some of them can leave glowing trails that remain visible for a couple of minutes. The shower has been declining in recent years. Halley’s Comet is near its greatest distance from Earth, so there aren’t as many bits of comet dust in this part of its orbital path. Even so, the shower could produce 20 or more meteors per hour at its peak. To watch the Orionids, find a dark but safe site away from city lights. Bundle up against the autumn chill, then sit back and watch the sparks from Halley’s Comet. Script by Damond Benningfield

Venus doesn’t have any moons. But it does share its orbit around the Sun. Astronomers have discovered 20 asteroids known as “co-orbitals,” but there could be many more. These big space rocks follow roughly the same path as Venus. But they won’t stay in that lane forever. And when they leave it, they could threaten Earth. These objects are nudged along by the gravity of Venus and the Sun. They generally stay well ahead of or behind Venus. Only one follows exactly the same orbit as the planet. The others move in and out a bit, getting closer to the Sun, then moving farther away. Over the long term, though, their orbits aren’t stable, so they can break free and head elsewhere. A recent study found that of the 20 known objects, six could threaten Earth within the next 12,000 years. And three of them are especially dangerous. All three are at least a thousand feet in diameter, so they could cause major damage if they hit our planet. A study also found that there could be many more of these Venus groupies. They stay so close to the Sun in our sky that they’re hard to see through the solar glare. And they move quickly, making them even harder to find. But a new telescope in Chile might pick out some of them – helping us find potential threats far in advance. Look for Venus near the Moon in the dawn sky tomorrow. It’s the brilliant “morning star,” so you can’t miss it. Tomorrow: an autumn meteor shower. Script by Damond Benningfield

California is the land of the stars. It’s also in the stars as the California Nebula – a cloud of gas and dust that looks like the outline of the state. It’s more than a thousand light-years away, in Perseus. The nebula belongs to a giant star-forming complex – the Perseus O-B-2 association. The region has given birth to many class O and B stars – the biggest and brightest of all stars. The California Nebula probably is energized by one of those stars, known as Xi Persei. The star is more than 30 times the mass of the Sun, and tens of thousands of degrees hotter. At that temperature, it produces huge amounts of ultraviolet energy. When that radiation zaps hydrogen atoms, it splits them apart. When they link back up, the atoms produce red light – the main color of the nebula. Oxygen and other elements produce their own colors, but they’re not nearly as common as hydrogen. The California Nebula probably is about a hundred light-years long. It’s likely to split into smaller clumps that will collapse to form even more stars. But radiation and winds from Xi Persei and other big stars will blow away much of the nebula’s material – limiting the number of new stars for this cosmic California. Perseus climbs into good view, in the northeast, in early evening. Xi Persei is visible to the naked eye, near the bottom of the constellation. But you need a telescope to see the faint outline of the California Nebula. Script by Damond Benningfield

Xi Persei doesn’t look all that imposing. The star shines at fourth magnitude, so it’s visible under dark skies, but not from cities and towns. But that’s only because it’s a long way off – about 1200 light-years. In reality, it’s one of the most impressive stars visible to the human eye. Perseus climbs the eastern sky on autumn evenings. It consists of a couple of ribbons of stars that join at Mirfak, the constellation’s leading light. And it contains the most famous variable star in the sky: Algol, the Demon Star, which fades and brightens every three days. Yet neither can compare with Xi Persei, which is near the bottom of the longer ribbon. At visible wavelengths, it’s about 13,000 times brighter than the Sun. But it’s tens of thousands of degrees hotter than the Sun, so it emits most of its light in the ultraviolet. When you add that in, Xi Persei is a quarter of a million times the Sun’s brightness. The key to that showiness is the star’s mass – roughly 30 times the Sun’s mass. At that great heft, gravity squeezes its core tightly, revving up its nuclear engine. Energy works its way to the surface, making Xi Persei hot and bright. Before long, it’ll get even hotter and brighter. It’ll explode as a supernova, briefly shining brighter than billions of normal stars – a brilliant demise for an impressive star. Xi Persei energizes a nearby cloud of gas, and we’ll have more about that tomorrow. Script by Damond Benningfield

For decades, Regulus had astronomers fooled. The star is bright, hot, and blue – an indication that it was quite young. Most estimates put its age at no more than a hundred million years – about two percent the age of the Sun. Instead, it’s at least a billion years old. But like a vampire, it’s been rejuvenated by taking the life’s blood of a companion, making it look much younger. The star we see as Regulus is about four times the size and mass of the Sun, and more than 300 times brighter. A few decades ago, astronomers discovered its companion – a “dead” star known as a white dwarf. The two stars are so close together that the corpse was hidden in the glare of the bright star. The presence of the companion means the system has to be at least a billion years old – old enough for the companion to evolve to its present state. As it evolved, it puffed up. Gas flowed from its surface over to the other star. That made the star we see today much bigger and heavier. It also made the star hotter, which made it bluer. Hot blue stars usually are quite young. So astronomers were fooled into thinking that bright Regulus was still a youngster – not an older star that’s been rejuvenated. Look for Regulus close to the Moon at dawn tomorrow. The distance between them will narrow as you move westward. They’ll be especially close as seen from Alaska or Hawaii. Script by Damond Benningfield

The Milky Way is a giant among galaxies – a hundred thousand light-years in diameter. But a few galaxies make the Milky Way look like a mere bauble by comparison. They span millions of light-years – puffed up by the action of supermassive black holes. These monsters are known as giant radio galaxies. Not only are they large, but they produce enormous amounts of radio waves. The black hole in such a galaxy’s heart is encircled by a massive disk. As material in the disk spirals into the black hole, magnetic fields fire “jets” of some of its particles like water from a firehose. These jets can streak far into space. They end as they plow into the material between galaxies, forming “lobes” that are bright sources of radio waves. A recent study found 15 of these giants. They’re in the constellation Sculptor, which creeps low across the south on October evenings. The largest of them spans more than 12 million light-years. The galaxy itself is wider and heavier than the Milky Way. But the jets puff up its overall size. It actually has two sets of jets – one nested inside the other. The longer set is older – powered up by the black hole millions of years ago. But the black hole might have slowed down its eating for a while, shutting off that flow of particles. Later, it started chowing down again, powering the second set of jets, which continue to expand – sustaining this galactic monster. Script by Damond Benningfield

Deneb, the brightest star of Cygnus, stands high overhead as night falls at this time of year. And it really is a brilliant star – tens of thousands of times brighter than the Sun. But if we could tune our eyes to see radio waves, Deneb wouldn’t even register. Instead, the swan’s leading light would be Cygnus A – one of the brightest radio galaxies in the universe. A radio galaxy produces huge amounts of radio waves. It’s usually a large elliptical galaxy, which looks like a fat, fuzzy football. It has a supermassive black hole at its center. Gas, dust, and stars spiral into the black hole. But powerful magnetic fields eject some of that material back into space. It forms “jets” that fire out at almost the speed of light. The jets can span hundreds of thousands of light-years. Electrons spiral through a jet’s magnetic field, producing radio waves. Eventually, the jets plow into gas and dust between galaxies, forming wide bubbles that emit even more radio waves. Cygnus A was the first radio galaxy ever discovered, in 1939. It’s about 760 million light-years away. Its black hole is two and a half billion times the mass of the Sun. The entire complex – galaxy, jets, and bubbles – spans more than 600,000 light-years. That’s six times the diameter of our home galaxy, the Milky Way – one of the biggest, brightest radio galaxies in our part of the universe. More about radio galaxies tomorrow. Script by Damond Benningfield

Floating through the clouds at Jupiter’s equator sounds like a celestial carnival ride. The equator spins at about 28,000 miles per hour – 28 times faster than Earth’s equator. So the Sun, moons, and stars would zip across the sky in a hurry. Jupiter is the largest planet in the solar system – 11 times Earth’s diameter. It also spins faster than any other planet – so fast that it bulges outward at the equator. At that speed, a day on Jupiter is less than 10 hours long. So the equator always sees about five hours of daylight followed by five hours of darkness. It might not sound right, but Jupiter spins so fast because it’s so big. As it swept up more material while it was taking shape, gravity compressed it, making it smaller. The planet had to spin faster to balance the books – like a skater spinning faster as it pulls in its arms. Some studies have suggested that Jupiter might actually have been slowed down early on by its magnetic field. The young planet was encircled by a disk of gas and dust that gave birth to its moons. As the gas swirled through the magnetic field, some of it developed an electric charge. The charged-up gas grabbed on to the field, acting like a brake – slowing down the solar system’s biggest and still fastest planet. Jupiter looks like a brilliant star below the Moon at dawn tomorrow. The twin stars of Gemini are closer to the left and lower left of the Moon. Script by Damond Benningfield

If you’d like to thank your lucky stars for a bit of good fortune, we have two stars for you to look at. They’re the brightest stars of Aquarius. Both of them have names that mean “lucky.” The brighter of the two is Sadalsuud. The name comes from an Arabic phrase that means something along the lines of “luckiest of the lucky.” When the name was bestowed, the star first appeared in the dawn sky around the spring equinox. The days were getting longer and warmer, and spring rains were settling in – bringing life-giving water to the fields. So the star was considered a sign of good fortune. The other lucky star is Sadalmelik – “luck of the king.” The exact reason for its name is unclear, although it, too, may relate to the seasons. Both stars are class-G supergiants. They’re about the same temperature and color as the Sun, but much bigger, heavier, and brighter. Both stars have passed through the prime phase of life, so their luck is running out – they’re nearing the end. Each will shed its outer layers and leave behind a massive white dwarf – a corpse about as heavy as the Sun, but only as big as Earth. Aquarius is in the southeast at nightfall. The “lucky” stars line up parallel to the horizon, with Sadalmelik on the left. The stars are separated by about the width of your fist held at arm’s length. But they’re so far from us that they don’t look all that bright – a bit of bad luck for skywatchers. Script by Damond Benningfield

Stars like the Sun go through several distinct phases of life, from embryo to corpse. Consider Aldebaran, the bright eye of Taurus, which accompanies the Moon tonight. It’s more than six billion years old – older than the Sun. And it’s well into “old age.” Aldebaran was born when a cloud of gas and dust collapsed. For millions of years, it shined as a result of the heat generated by that collapse – its “embryonic” phase. Eventually, its core got hot enough to ignite the fires of nuclear fusion, and Aldebaran entered the prime phase of life – fusing hydrogen to make helium. A few hundred million years ago, it used up the hydrogen in the core. The core got smaller and hotter, and Aldebaran began fusing the hydrogen in a shell around the core. At the same time, its outer layers puffed up, so Aldebaran is more than 40 times wider than the Sun. This is the giant phase of life. Eventually, the core will get hot enough to fuse the helium to make carbon and oxygen. But when the helium is gone, fusion will stop. The core will get smaller and hotter, and its radiation will push the star’s outer layers into space. Only the hot, dead core will remain – a white dwarf. Even that isn’t the end, though. The white dwarf will cool and fade. Hundreds of billions of years from now – and perhaps much longer – it’ll stop producing any visible light at all. That will make it a black dwarf – the final stage for the eye of the bull. Script by Damond Benningfield

The Moon barrels through the Pleiades star cluster this evening. It’ll pass directly in front of the cluster, briefly blocking most of its stars from view. The Pleiades is the most famous of all star clusters. It’s also known as the Seven Sisters, but under dark skies – with no Moon in the way – you might actually see nine stars or more. But that’s only the beginning. The cluster contains more than a thousand stars. In fact, it was the first cluster to be recognized as a cluster – a group that’s moving through the galaxy together. That recognition came in 1767. John Mitchell, a clergyman and scientist, was looking at several tightly packed groups of stars. He studied the Pleiades in the greatest detail. And he calculated that there was only a one-in-500,000 chance that the grouping could be random. Instead, something had to be holding the stars together. His idea was confirmed when astronomers measured the motions of the cluster’s stars. They’re all moving in the same direction, and at the same speed. Today, we know that’s because they were born together, from a single giant complex of dust and gas. They’re bound to each other by their mutual gravitational pull. But they won’t stay together. The cluster is being pulled apart by the gravity of the rest of the galaxy. So the Pleiades probably will dissipate in about 250 million years – with its member stars going their own way. Script by Damond Benningfield

An embryonic star may be about to vanish – perhaps for a century. It’s not going anywhere. Instead, it’ll be cloaked by a dense cloud that encircles two companions. T Tauri is the prototype for a class of proto-stars. The gravity of such a star is causing it to collapse, making it hot and bright. But its core isn’t hot enough to ignite the fires of nuclear fusion, so it’s not yet a true star. The star we see as T Tauri is about twice as massive as the Sun. It’s encircled by a disk of gas and dust – the raw materials for making planets. And it might already have given birth to at least one planet. T Tauri is a member of a triple-star system. Its companion stars are close together, encircled by their own disk. It’s so thick that it hides the stars at visible wavelengths – we see them only in the infrared. Now, the companions and their disk are starting to slide between us and the brighter star. The star has faded a good bit in recent years. Eventually, it may be hidden behind the disk as well. And it could take a century for the disk to move out of the way – allowing the brightest star of the T Tauri system to shine through once more. Taurus is low in the east and southeast by late evening. T Tauri is just above Aldebaran, the bull’s brightest star, far to the lower left of the bright Moon. The young star is visible through a telescope – for now. More about the Moon and the bull tomorrow. Script by Damond Benningfield

The bull is charging into the evening sky. Taurus is in full view by about 11 o’clock, low in the east. He stands high in the south before dawn. He’s rising earlier each night, and will be in view all night long by about Thanksgiving. All the stars rise four minutes earlier each night – a result of Earth’s motion around the Sun. Earth makes one full turn on its axis against the background of distant stars every 23 hours and 56 minutes. So, if you looked at the sky every 23 hours and 56 minutes, and you could see through the daytime glare, you’d always see the same stars in the same position. But during that period, Earth moves along its orbit around the Sun. The distance it covers means the planet has to turn four extra minutes for the Sun to reach the same position in the sky. That makes a day 24 hours long. And it also means that the background stars rise and set four minutes earlier on our 24-hour clock. As a result, every star and constellation is in prime evening view at different times of the year. For Taurus, it’s fall and early winter – the time the bull charges across the evening sky. For now, look for Taurus beginning in late evening. Its brightest star is Aldebaran, the bull’s eye. His face is outlined by a V-shaped pattern of stars to the upper right of Aldebaran. And his shoulder is the sparkly little Pleiades star cluster, well above Aldebaran. More about Taurus tomorrow. Script by Damond Benningfield

The Moon is full tonight, and it’s especially bright as well. And to top things off, it’s the most famous full Moon of them all – the Harvest Moon. Harvest Moon is the full Moon closest to the fall equinox, so most years it falls in September. But once every five years or so it skips into October. This year, September’s full Moon came 15 days and 10 minutes before the equinox, which took place on the 22nd. This month’s full Moon comes 14 days, 9 hours, 29 minutes after the equinox, so it barely takes Harvest Moon honors. The Harvest Moon was important in earlier times because it shined over the fields when crops were ready to be brought in. Its light allowed farmers to work into the night. And because of the angle of the Moon’s path at this time of year, the full Moon rises only a few minutes later each night as seen from more northerly latitudes. So it’s almost like having a full Moon for several nights in a row. People often think that the Harvest Moon must be especially bright, but that isn’t usually the case. This year, however, it is. That’s because it comes less than a day and a half before the Moon is closest to Earth for its current orbit – roughly 15,000 miles closer than average. That provides some especially bright nights for farmers – and the rest of us, too. Tomorrow: the bull charges into the evening sky. Script by Damond Benningfield

It’s pretty easy to measure the length of a day on Mars or most other solid bodies. Just pick a feature on the surface and see how long it takes to spin back into view. It’s not so easy for planets that don’t have a solid surface. We can track bands of clouds, but different bands can move at different speeds. That’s been an especially tough problem for Saturn, the second-largest planet in the solar system. Scientists have been trying to pin down its rotation rate – the length of its day – for centuries. When the twin Voyager spacecraft flew past Saturn in the 1980s, they measured the planet’s magnetic field to reveal the rotation rate of its interior. But when the Cassini spacecraft orbited Saturn decades later, its observations showed the day was about six minutes longer. At the end of its mission, Cassini flew between Saturn and the inner edge of its rings. Measuring waves in the rings and tiny changes in the planet’s gravitation field produced yet another length: 10 hours, 33 minutes, and 38 seconds. That’s not necessarily the final answer. Scientists continue to study the giant planet to know how to set their Saturn clocks. And Saturn is in great view tonight. It looks like a bright star quite close to the lower right of the Moon at nightfall, and below the Moon as they set, before dawn. Script by Damond Benningfield

Saturn and Venus bracket the pre-dawn sky now. As Saturn drops from view in the west, Venus nudges into view in the east. Saturn looks like a bright star, while Venus is the brilliant morning star. The planets are both sliding eastward against the background of distant stars. Saturn lined up opposite the Sun a couple of weeks ago. For a few months around that point, the planet looks like it’s “backing up” against the background of stars – a result of the relative motions of Saturn and Earth. Earth is closer to the Sun than Saturn is, so our planet moves faster. It overtakes Saturn every 13 months, making Saturn appear to shift into reverse. It’s actually still moving in its usual direction – only our viewing angle is changing. It’s like passing another car on the highway. For a while, the other vehicle looks like it’s moving backward against the background of buildings and trees. When you move far enough past it, though, it appears to resume its normal forward motion. Saturn will end its backward motion and shift back into forward at the end of November. Venus, on the other hand, is about to pass behind the Sun as seen from Earth, so it’s dropping closer to the Sun every day. That’s also a result of the orbital motions of the two planets. Venus will disappear in the twilight in December, and cross behind the Sun in January – depriving us of the “morning star.” More about Saturn tomorrow. Script by Damond Benningfield

Scientists don’t know what dark matter is. But they have some ideas of what it isn’t. And they took a big step in ruling out some possibilities with the release of a study last year. Dark matter produces no energy – the reason it’s described as “dark.” But we know it’s there because its gravity pulls on the visible matter around it. In fact, it appears to make up about 85 percent of all the matter in the universe. The leading idea says dark matter consists of some kind of subatomic particle. A top candidate is called a WIMP – a weakly interacting massive particle. Although dark matter almost never interacts with normal matter, it might occasionally do so – ramming into the nucleus of a normal atom. That would produce a tiny spark of light, which detectors might see. One experiment is LUX-ZEPLIN. It’s in a former gold mine, almost a mile below the town of Lead, South Dakota. The rock above it blocks other types of particles from reaching the experiment. Its detectors are inside a vat filled with about 8,000 tons of liquid xenon. The hope is that a WIMP will hit a xenon molecule and trigger that spark of light. Project scientists conducted 280 days of observations. And they didn’t find any indication of WIMPs. But their test was the most sensitive yet for certain types of WIMPs. So the experiment rules out some candidate particles – narrowing the possibilities for dark matter. Script by Damond Benningfield

At first glance, the dwarf planet Ceres doesn’t seem like a friendly home for life. It’s small, dark, and scarred by impact craters. Yet a deeper look presents a more optimistic picture. It has more water than any body in the inner solar system besides Earth. It has an abundance of organic compounds – the chemical building blocks of life. And it should be warm enough below the surface to sustain microscopic life. Ceres is the largest member of the asteroid belt – a wide band of debris between the orbits of Mars and Jupiter. It’s about a quarter the diameter of the Moon. It probably consists of a dense core and mantle surrounded by an icy crust. The Dawn spacecraft studied Ceres from orbit a decade ago. It saw big patches of bright, salty minerals. It also saw mountains, including one that’s three miles high; if you scaled Ceres to the size of Earth, the mountain would be 40 miles high. And the craft discovered that much of the surface consists of minerals that formed in a wet environment. So Ceres has water, heat, and organic compounds – the basic ingredients for life in what looks like an unfriendly world. Ceres is at a point called opposition – it lines up opposite the Sun in our sky. That means it rises around sunset and is in view all night. It’s also closest to us at opposition, so it shines at its brightest. Even so, you need binoculars or a telescope to pick it out, in the constellation Cetus. Script by Damond Benningfield

The constellations are well armed. Several of the star patterns that depict people or gods are carrying weapons. And some of them are in good view at this time of year. As darkness falls, look low in the west for the brilliant star Arcturus. It stands at the base of Boštes the herdsman. Like many of the ancient star figures, Boštes has different stories, and is drawn in different ways. In most depictions, he’s holding something long and straight against his right side. In some cases, it’s a staff. But in others, it’s a spear. Well above Boštes is Hercules, marked by a lopsided box of four stars. He’s wrestling the multi-headed hydra. And in some depictions, he’s holding up a club. In the south, look for Sagittarius. To modern eyes, it forms the outline of a teapot. But to the ancients, those stars formed an archer. The star at the outer edge of the spout is the point where he’s gripping both bow and arrow. And low in the northeast there’s a figure with a unique weapon. Perseus the hero is holding the head of Medusa. In mythology, anyone looking at Medusa was turned to stone. Perseus managed to sever the head, then used it to save the princess Andromeda from a monster. And if you’re stargazing before dawn, there’s another armed figure, well up in the south: Orion the hunter. He has two weapons. He’s holding a club in an upraised arm, with a sword strapped to his belt – a heavily armed figure in the stars. Script by Damond Benningfield

The star Fomalhaut is a bit of a disappointment. Almost two decades ago, astronomers announced the discovery of a giant planet orbiting the star – the first exoplanet actually seen at visible wavelengths of light. Almost from the beginning, though, other astronomers questioned the discovery. And they were right. It wasn’t a planet at all, but a big clump of dust – the aftermath of a giant collision. Fomalhaut is about twice as big and heavy as the Sun, and quite a bit brighter. It’s encircled by wide bands of dust. Most of the dust is at least a hundred times the distance from Earth to the Sun. Fomalhaut is only about one-tenth the age of the Sun. Even so, it’s old enough that it should have blown away most of the dust. The fact that the belts are so prominent – especially the outer belt – means that they’re being renewed. The most likely source is collisions between large comets or asteroids. As those bodies are destroyed, they spew dust out into space. One estimate says it would take the destruction of 2,000 comets that are one kilometer in diameter every day to keep the belts going. The would-be planet was the result of a collision between two even larger objects – briefly creating the illusion of a giant planet around this bright star. Fomalhaut is low in the southeast at nightfall, and climbs across the south later on. Script by Damond Benningfield

The southern evening sky is pretty bare at this time of year – lots of dark, empty spaces, but few bright stars. The one notable exception is Fomalhaut. It’s the brightest star of Piscis Austrinus, the southern fish. It’s low in the southeast at nightfall, and arcs across the south later on. The star we see as Fomalhaut is 25 light-years away. It’s about twice as big and heavy as the Sun, and more than 15 times brighter. It’s young – about 10 percent the age of the Sun. And it’s encircled by wide bands of dust, which may contain planets; more about that tomorrow. Fomalhaut has two companion stars – bound to it by their mutual gravitational pull. Both stars are smaller, cooler, and fainter than the Sun. One of them is barely visible to the eye alone, but you need a telescope to see the other. Both stars are a long way from Fomalhaut itself. One is almost a light-year away, while the other is two and a half light-years. Astronomers know they’re bound to Fomalhaut because they’re moving in the same direction and at the same speed. Their composition is similar to Fomalhaut’s as well, and so is their age. Fomalhaut itself will shine for another few hundred million years. But the companions will last much longer – billions of years for the larger one, and hundreds of billions of years for the other. So they’ll still be shining across the galaxy long after the demise of their showy companion. Script by Damond Benningfield

The Andromeda Galaxy, M31, is encircled by dozens of satellites – smaller galaxies in orbit around it. One of the larger satellites is something of an oddball. Of the three-dozen brightest, it’s the only one that lines up on the far side of Andromeda as seen from our home galaxy, the Milky Way. M31 is the closest giant galaxy to the Milky Way – just two-and-a-half million light-years away. Messier 110 is a couple of hundred thousand light-years farther. It’s a few thousand light-years in diameter, and contains about 10 billion stars – a tiny fraction the size of Andromeda. Astronomers have spent years watching M31’s entourage with Hubble Space Telescope. They recently reported that 36 of the 37 brightest members line up on the side of M31 that faces the Milky Way. And that’s hard to explain. The study said there’s only a tiny chance that the alignment is a coincidence – there must be a reason for it. But no one knows what that reason might be. It’s not a result of the Milky Way’s gravitational pull – it’s not strong enough. So there’s no obvious explanation for why M110 is an oddball – lurking on the far side of M31. M31 is low in the northeast at nightfall. Under dark skies, it looks like a hazy slash of light about as wide as the Moon. Through a small telescope, M110 looks like a bright star close by. Script by Damond Benningfield

Earth has only one moon – one large natural satellite. But it might travel with an entourage of Moon chips – bits of the Moon blasted into space by impacts with asteroids. Some of the chips may share Earth’s orbit around the Sun. Others become “quasi”-moons. They weave around the Sun in a way that looks like they’re orbiting Earth. Astronomers have catalogued a dozen or more quasi-moons in recent years. The smallest is the size of a house. The largest is about three miles across. A recent study looked at how easy it would be to make a quasi-moon as the result of an impact. The study team simulated tens of thousands of impacts across the entire Moon, at different lunar phases and with different ejection speeds. The results showed that it’s pretty darned easy. Almost seven percent of the simulations produced objects that share Earth’s orbit. And two percent became quasi-moons. They can remain in stable orbit near Earth for thousands of years before they’re kicked away. A Chinese spacecraft is scheduled to visit one of the quasi-moons next year. It’ll collect a few ounces of dirt and pebbles and return them to Earth for study. That should tell us whether the object is a chip off the ol’ Moon, or an interloper from elsewhere in the solar system. The Moon has a bright companion tonight: Antares, the brightest star of Scorpius. It’s close to the right of the Moon as they drop down the western sky in early evening. Script by Damond Benningfield

The closest giant galaxy to the Milky Way is Messier 31, the Andromeda Galaxy. It’s two-and-a-half million light-years away. But it’s getting closer – by about 250,000 miles every hour. For more than a decade, in fact, it’s looked like the two galaxies were on a collision course. But a recent study says there’s only a 50-50 chance of a collision and merger. And if it does happen, it’ll take place billions of years later than previous estimates. The new study used years of observations by two space telescopes – Hubble and Gaia. Researchers plugged those observations into simulations that also considered the gravitational effects of two smaller galaxies. The results indicated that one of them tends to push Andromeda and the Milky Way together, while the other tends to pull them apart. The researchers ran a hundred thousand simulations. In half of them, Andromeda and the Milky Way flew past each other and went their own ways. In the other half, they eventually spiraled together and merged – but not for at least 10 billion years – twice as long as earlier estimates. The simulations aren’t the final word – there are just too many uncertainties. But for now, it seems likely that the two giants will stay apart for a long, long time. M31 is in the northeast at nightfall. Under dark skies, it’s visible as a hazy patch of light. Binoculars make it easier to pick out. Script by Damond Benningfield

Messier 31, the Andromeda Galaxy, is the largest and most-distant object that’s easily visible to the unaided eye. Under dark skies, it looks like a skinny cloud about as wide as the Moon. Right now, it’s about a third of the way up in the northeast at nightfall. M31 is two-and-a-half million light-years away. In other words, the light you see from the galaxy tonight began its journey across the cosmos two-and-a-half million years ago. The galaxy is roughly 150,000 light-years across – bigger than the Milky Way – and may contain a trillion stars. It’s also the hub of its own galactic empire – it’s orbited by more than three dozen smaller galaxies. And a recent study revealed many new details about the satellites. Astronomers spent years looking at them with Hubble Space Telescope. And they supplemented the new observations by going through older ones. They found that most of the stars in the smaller galaxies had been born by about 12 billion years ago – when the universe was about one-tenth of its present age. And star formation had all but stopped by about eight billion years ago. Galaxies that are bigger and farther from M31 gave birth to stars a little longer than those that are small and close. One of the bigger satellites might have rammed through M31 a few million years ago. That stirred things up throughout the empire surrounding big, beautiful M31. More about M31 tomorrow. Script by Damond Benningfield

People become astronomers for many reasons: They’re interested in the workings of the stars, or the quest to find life in the universe, or the fate of the universe itself. Geoffrey Burbidge joked that he became an astronomer because he married one. He and his wife, Margaret, were astronomy’s power couple. And they co-authored one of the most important studies of the 20th century. Burbidge was born 100 years ago today, in the English village of Chipping Norton. He first studied history, but switched to physics. After earning his undergraduate degree, shortly after World War II, he developed bombs for a while. Back in academia, he married Margaret, and they hopped around England and the United States over the next few decades. Burbidge contributed to many areas of astronomy theory. But he’s best known for a single paper, known as B-squared-F-H for the names of its authors – the two Burbidges, William Fowler, and Fred Hoyle. In it, they explained how stars forge most of the elements in the universe. Many elements are created in a star’s core during its long life; others, in the violent deaths of stars. Some of the elements are expelled into space, where they can be incorporated into new stars. The newer generations make even more elements – eventually creating the chemistry we see in the universe today. So the paper showed that we’re all made of “starstuff” – elements created in the stars. Script by Damond Benningfield

Neptune is one of the giants of the solar system. But it’s so far away that it’s tough to study. We know little about its interior. And much of what scientists think they know comes from lab experiments and computer models. Neptune is the Sun’s most remote major planet. So although it’s almost four times Earth’s diameter, it’s a tiny target for telescopes. And only one spacecraft has ever visited the planet – Voyager 2, in 1989. From those observations, along with those from telescopes on the ground and in space, scientists have developed a model of how Neptune is put together. It probably has a dense, rocky core, surrounded by an “ocean” of super-heated water, ammonia, and methane. The pressure squeezes this layer so tightly that the compounds act like ice. Around that is a layer of hydrogen, which is topped by a methane-rich atmosphere. The methane absorbs red light, giving the planet a blue-green color. It’ll be decades before another mission can approach Neptune. Until then, we’ll have to rely on a lot more calculations to understand this remote giant. Neptune is at its best right now. It’s in view all night and it’s brightest for the year. Even so, you need a telescope to spot it. But you can easily spot its location. As night falls, look for Saturn, which looks like a bright star, low in the east. Neptune is to the left of Saturn, by a bit more than a finger held at arm’s length. Script by Damond Benningfield

Earth “falls” into a new season today – astronomically speaking. It’s the September equinox, when the Sun crosses the equator from north to south. It marks the start of autumn in the northern hemisphere, and spring in the southern hemisphere. On the equinoxes, neither the north pole nor the south pole tips toward the Sun, so night and day are roughly the same length in both hemispheres – about 12 hours between sunrise and sunset. We say “roughly” because there are a couple of caveats. One is the way we calculate the times of sunrise and sunset. For the days to be truly equal, we’d have to mark the times when the Sun is bisected by the horizon – half in view, half still hidden. But we don’t. Instead, sunrise is the moment when the Sun first peeks into view, and sunset is the moment when the limb of the Sun drops from view. That adds a couple of minutes to the day. The other correction factor is Earth’s atmosphere. It “bends” the sunlight above the horizon. So when we see the Sun standing just atop the horizon, it’s actually a little below it. That combination adds a few minutes to the equinox “day.” So at the equator, daylight lasts for 12 hours plus six and a half minutes. At 30 degrees north – the latitude of Austin – it’s 12 hours and eight minutes. And at 60 degrees – roughly the latitude of Anchorage – it’s 12 hours and 16 minutes – an extra dose of sunlight as we fall into autumn. Script by Damond Benningfield